There are three basic types of light sources used today--incandescent, fluorescent and high-intensity discharge lamps. Incandescent lamps produce light by electrically heating high resistant tungsten filaments to intense brightness. Fluorescent lamps produce light by establishing an arc between two electrodes in an atmosphere of very low pressure mercury vapor in a chamber (the glass tube). High-intensity discharge type lamps produce light by establishing an arc between two electrodes but with the electrodes only a few inches apart--in opposite ends of a small, sealed, translucent or transparent arc tube.
Incandescent general lighting lamps produce from 17 to 23 lumens of light per watt of power consumed dependent upon wattage, life and physical design features. The bulk of the radiant energy from incandescent light lies in visible and infrared region of the spectrum. Incandescent lamps follow established physical laws of thermal emission; energy is distributed in a smooth curve beginning at or near the UV range with very little deep blue radiation, increasing with wave length into the deep red.
Incandescent lamps use tungsten filaments, usually comprised of coiled tungsten wire heated to incandescence by an electrical current when the lamp is operating. Coiling the coiled filament increases its light producing efficiency. Filling inert gas (as compared to normal atmospheric gases) in the lamp envelope reduces tungsten evaporation and allows higher operation temperature of the filament.
Gases of helium, neon, argon, krypton, radon, and xenon are elements which constitute a group of inert gases, or noble gases, because of their extreme reluctance to form chemical compounds. Neon and argon are used in lighting tubes such as arc discharge tubes. The chief use of neon is in the arc discharge tubes, and the chief use of argon is to fill ordinary domestic light bulbs which usually contain a mixture of about 93% argon and 7% nitrogen.
Xenon is an element (symbol Xe) member of the noble gas group and has an atomic number of 54 and atomic weight of 131.30. It is colorless and has a boiling point of -108.degree. C. (one atmosphere), is noncombustible, nontoxic and nonreactive. Its chief use is in photographic flash lamps, luminescent tubes and lasers, and also as an anesthetic. Xenon is commonly used to fill high-intensity arc lamps and in discharge tubes capable of producing high-intensity flashes of a very short duration. Such tubes are employed in electronic flash apparatus used in photography. Unlike helium, neon, and argon, xenon does form a few chemical compounds, for example, xenon tetrafluoride (XeF.sub.4) and xenon oxide (XeO.sub.3).
Halogens are a group of elements which, in a gaseous phase, are used to fill lamp bulbs, iodine being the most common. A halogen lamp produces greater luminosity than a nitrogen argon filament lamp. The quartz-halogen bulb, widely used for car headlights and projector bulbs, is a tungsten filament lamp operating at very high temperatures in iodine vapor. As the lamp burns, the gas combines with tungsten atoms that boil off the filament, and as it circulates inside the bulb, deposits the tungsten back onto the filament rather than on the bulb wall. This keeps the bulb wall clean and allows the lamp to deliver essentially its initial light output throughout life. Halogen bulbs have wall temperatures of at least 500.degree. C. hotter than standard bulbs. These, of course, require the use of quartz rather than glass, dictated by the high temperature requirements.
A festoon style lamp is one that is suspended between two points, typically the end points of an elongated, cylindrical glass tube filled with a gas and having a filament, typically tungsten, coincident with the longitudinal axis of the cylindrical bulb. The lamp is held in place by conductive spades dimensioned to receive the two end cap/conductors of the lamp and to energize the same. The base of the lamp connects the lamp to the electric circuit and also provides an easy method of mounting the lamp and replacing it. The base or end caps are made of aluminum or nickel-plated brass. The bases are insulated from each other by the glass tube.
A typical incandescent tungsten filament festoon style lamp with a glass bulb (such as those identified as "Low Voltage Lamps" in the Lucifer Lighting Technical Information Guide, page 2) operates at a line voltage of 12 or 24 volts and will produce a color temperature of about 2,450.degree. Kelvin, lumen output of 10 (3 watts), 37 (5 watts), or 75 (10 watts) with a lamp life (rated) of about 1,450 hours. This lamp has a tungsten filament and is filled with a mixture of 93% argon and 7% nitrogen. The same lamp filled with xenon gas will produce a color temperature of 2,620.degree. K. at a lower lumen output, but will increase the lamp life (computed) to over 20,000 hours (5 watt/12 volt) or over 25,000 hours (5 watt/24 volt). For comparison purposes, the halogen lamps of approximately the same size will produce a color temperature of 3,000.degree. K. and are rated at 1,000 hours (24 volt) and 2,000 hours (12 volt).
The increase in xenon lamp life is obtained by operating the lamp at voltages below the design voltage (test voltage in Table I, infra); to wit, the 12 volt xenon lamp being operated below its 13.5 design voltage and the 24 volt xenon lamp being operated below its 28 volt design voltage. These computed lamp lives for the xenon lamp are based on an equation used to calculate the effect of a change from the design voltage on lamp life as published in the Illuminating Engineering Society Lighting Handbook Reference Volume 1984.
The importance of the xenon lamp is then primarily in the increased lamp life and secondarily, in the higher color temperature. Because festoon lamps are used in series in strip lighting fixtures, often where there may be up to hundreds or thousands of bulbs, such as display cases for department stores, ceiling cove lighting in large commercial and residential applications, stair rail and stair step lighting, etc., where it becomes very important for maintenance purposes that lamp life periods be of as long duration as possible. Here, the radical increase in lamp life decreases by many times the lamp maintenance, and attendant cost to service and replace lamps. This is especially important when, as here, one has a multitude of lamps to a single lighting fixture. With lamp lives of greater than 20,000 hours, the xenon lamps need only be replaced at intervals of two to five years.
The lamp of the present invention is used to form strip lighting as opposed to lamps which produce light from a point source. Thus, the lamp of the present invention is designed to be used with, for example, the Lucifer Lighting Series 2000 strip lighting system.
Heretofore, no festoon style lamp has been available that contains xenon gas. The benefits of using xenon according to the teachings of the present specification is that it will result in higher color temperature (up to 2,620.degree. K.) than traditional incandescent lamps, with extended lamp life up to four or five times beyond that of the presently available lamps, while operating at warmer temperatures than halogen lamps.